Serena quits opener as Henin wins

MADRID, Spain -- Serena Williams was forced to quit her opening match at the season-ending WTA Championships against Russian Anna Chakvetadze with a knee injury on Wednesday.

American Williams was treated by the tournament doctor before the start of the ninth game and pulled out having lost the first set 6-4 in Madrid.

The fifth-ranked Williams has reached the final in all three previous appearances at the event, which features the top eight players.

If Williams is not fit to face Henin on Thursday, Wimbledon finalist Marion Bartoli will replace her for the last two matches of the round-robin tournament.

Earlier defending champion Justine Henin cruised past Jelena Jankovic 6-2 6-2, breaking serve six times to win her 22nd straight match.

Victory saw her improve to 9-0 against the third-ranked Serbian who is making her debut at the tournament which features the top eight players.

"It has been almost the perfect schedule for me playing at six o'clock every night because that enables me to get good rest," said 25-year-old Henin.

"I was much better today than yesterday. I was in a good rhythm and much more aggressive.

"Perhaps I can keep coming to the net a little more and I can work on my serve, but I can be happy with what I did today."

The Belgian, who will finish the campaign as world number one for the second year in a row, had opened her Yellow Group program with a 6-1 7-6 (7-4) victory over Chakvetadze.

Later Wednesday Ana Ivanovic takes on Daniela Hantuchova. E-mail to a friend